Home Forums Main YANAP Discussion Forum A really great read… Reply To: A really great read…


This evening’s class was cancelled. So I got out a couple of lenses and a ruler.  This is not too scientific but is interesting anyway.

I have a Canon 100 mm macro lens and a Sigma 150 mm macro lens, so I decided to see what happens at the macro end of things.  I set up a tripod and mounted a 5D Mk III using the body’s socket.  I put on the 100 mm lens and pointed it at a ruler.  I was trying to get the ‘5’ in focus and managed to miss, but I’m not sure how much that matters.  The mm scale is more interesting because the marks are closer.  I set a flash and took a photo.  Then I changed to the 150 mm lens and moved the tripod back a bit and elevated it some more to try to increase the distance but keep the alignment of the ruler about the same.  And, I got another shot, with focus on the ‘5’.

I put a few photos on Flickr, this one is a merge of two 100% crop photos with some masking so the visible parts can be at 100% opacity.  And I drew a couple of red horizontal lines.


The masked bits are from the 100 mm photo.  It’s interesting that even moving the 150 back a bit, the character size and ruler width are larger in the 150 mm photo, and I seem to have about a milometer more DOF, too!  Plus, the DOF area in the frame is larger as well!

What works for macro may not work as well at longer distances with larger subjects.  Macro is nice because the fall off of DOF is so sharp.  Additional photos are needed to ensure consistent results, but in this case a longer lens from a bit further back seems to have delivered more DOF even with a slightly larger subject.